The KSTAR neutral beam injector provides up to 10 MW of plasma heating power, and secondary electrons generated from the acceleration grids can produce significant thermal loads inside the ion source. An electron dump (E-dump) is installed to dissipate this heat and prevent damage. In this study, the total heat load on the E-dump was experimentally measured using a water-cooled calorimetric diagnostic, and numerical simulations were performed to evaluate the heat-flux distribution under the cusp magnetic field configuration. While removing the E-dump magnets could reduce the peak heat flux, the magnets were retained to avoid the associated risk of arc-efficiency degradation. Instead, the E-dump cooling-water channels were enlarged, resulting in significantly improved heat removal performance while maintaining the original cusp magnetic field configuration.